1. Field of the Invention
The present invention relates to a system for providing infinitely variable valve lift for power cylinder poppet valves in a reciprocating internal combustion engine.
2. Disclosure Information
Designers of reciprocating internal combustion engines have sought to employ variable valve lift systems. Such systems have been largely driven by a desire to achieve better fuel economy and driveability in the face of increasingly stringent emission and fuel economy requirements. Not surprisingly, several variable lift mechanisms have been proposed by various designers. These proposed designs range from extremely complicated mechanical systems such as that shown in SAE Technical Paper 2000-01-1221, to more straightforward systems such as that shown in SAE Technical Paper 970334. The system shown in SAE 970334 includes a hollow rocker arm having a geared rack and movable pinion shaft which translates so as to cause adjustment of the rocker arm lift ratio. Unfortunately, such a system would suffer from packaging problems because the volume of the system is too great. And the functionality of the system presents issues insofar as it is necessary to use a geared interface between the rocker arm and the geared movable pinion shaft.
The present system offers valve lift control with a straightforward design, good packageability and excellent function.
A variable lift cylinder valve system for internal combustion engine includes at least one poppet valve disposed within a cylinder head of an engine, with the poppet valve having a head and a stem adapted for contact by a valve opening member. A spring biases the poppet valve into a closed position. At least one valve operating camshaft is mounted in the engine. The camshaft carries at least one cam lobe. A rocker arm is in contact with both the cam lobe and the valve stem. A translational pivot which is in contact with the rocker arm converts a linear component of motion of the cam lobe into rotational motion of the rocker arm and corresponding linear motion of the poppet valve. A control shaft extending along an axis generally parallel to the axis of the camshaft is mounted for pure rotation about the control shaft axis. A control arm mounted upon the control shaft and operatively connected with the translational pivot converts the rotational motion of the control shaft into translational motion of the pivot so as to control the lift ratio of the rocker arm. In this manner, the lift of the valve is infinitely controllable between a condition of no lift at all i.e. the closed position, and full lift. In essence, the system uses a range of composite positions in which the camshaft, cam lobe, rocker arm, and control arm are configured so as to cause valve lift to range from no lift at all to maximum lift.
In order to achieve proper control of the valves according to a system of the present invention, the control arm and control shaft cannot rotate independently. This fact provides an opportunity to accurately calibrate the minimum lift position of the variable lift cylinder valve system claimed herein. In essence, during calibration, the camshaft is placed in a predetermined rotational position, whereas the cylinder valve being calibrated is placed in a predetermined position vis-à-vis the valve seat. Then, the control arm is locked to the control shaft in the position which the rocker arm assumes as a result of the predetermined camshaft and cylinder valve positions.
It is an advantage of the present invention that notwithstanding its variable valve lift capability, a system and method according to this invention uses a conventional camshaft which provides a reliable means for actuating valves in an engine.
It is a further advantage that the present system is readily retrofittable into existing engine designs. This obviates the need for extensive retooling of cylinder heads.
It is a further advantage that the system of the present invention achieves variable lift control with simple kinematics and relatively few moving parts, which reduces the cost of manufacturing and improves the accuracy of valve lift control.
It is a further advantage of the present invention that this system reduces the coefficient of variation of the indicated mean effective cylinder pressure (IMEP), particularly at idle. It is well known to those skilled in the art that variation of IMEP at idle is extremely detrimental to idle stability. Thus, it is very advantageous that the present system provides a means to accurately calibrate the valve lift, particularly lifts in the range used during engine idle.
It is a further advantage of the present invention that the present system and method are adaptable to engine control strategies having varying complexity and technical sophistication.
Other advantages, as well as features and objects of the present invention, will become apparent to the reader of this specification.